This invention relates generally to tube testing apparatus, and more specifically to a gas tube tester for testing both the breakover voltage and the leakage current of cold cathode gas discharge tubes. While the gas tube tester disclosed herein is directed primarily to a tester for testing gas tubes used in telephone line communications systems, it will be understood that other types of gas tubes may be tested.
Line protectors are used in the telephone line circuit to protect against overvoltage and overcurrent conditions which may occur should a power line or lightning bolt strike a telephone line. In many instances these line protectors include carbon elements which provide an arc-over gap. However, many line protector devices are of the type utilizing gas discharge tubes.
Gas discharge tubes are primarily used in line protecting devices located at the central office. The gas discharge tube line protector is a relatively expensive device and its reliability must be insured because of the large quantity of expensive telephone switching equipment to be protected at central office stations. Therefore, the gas discharge tube must be periodically tested to determine its reliability.
One gas discharge tube of the type which can be tested by the apparatus of this invention is disclosed in U.S. Pat. No. 3,755,715, which is assigned to the same assignee of record. It will be understood that other gas discharge devices can be tested with the apparatus of this invention.
Heretofore, testing of gas discharge tubes involved only a breakdown voltage test to determine the breakover voltage at which the gas tube would ionize. While this would give some indication of the relative quality of the tube, a leakage test would also indicate an important quality factor of the tube and would allow a technician to make a better determination of the possibility of further use of the gas discharge tube in a line protector. However, heretofore, leakage devices for gas discharge tubes have been almost nonexistent because of the complexity and high cost of such testing equipment. This complex and expensive equipment, furthermore, was relatively large and could not be portable so that technicians in the field could have ready access to a gas discharge tube tester.